CHAPTER SECTION 2 Ionic And Covalent Bonding

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NameCHAPTER 6ClassDateThe Structure of MatterSECTION2 Ionic and Covalent BondingKEY IDEASAs you read this section, keep these questions in mind: Why do atoms form bonds?How do ionic bonds and covalent bonds differ?What gives metals their distinctive properties?What makes a polyatomic ion different from other ions?Why Do Chemical Bonds Form?Atoms form bonds when their valence electronsinteract. Recall that atoms with filled outermost energylevels are more stable than atoms with partially filledenergy levels. In general, atoms join to form bonds sothat each atom has a stable electron configuration.In other words, each atom binds in order to fill itsoutermost energy levels.There are two basic kinds of chemical bonding: ionicbonding and covalent bonding. The type of bonding in a compound determines many of the properties of the compound.READING TOOLBOXCompare As you read, makea chart that describes andcompares the different typesof bonds.READING CHECK1. Explain Why do atomsjoin to form bonds?A Comparison of Ionic and Covalent CompoundsIonic compoundsCovalent compoundsStructurenetwork of bonded ionsmoleculesValence electronstransferredsharedElectrical conductivitygood (when melted ordissolved)poorState at roomtemperaturesolidsolid, liquid, or gasMelting and boilingpointsgenerally highgenerally lowEHHDBG@ EHL K 2. Compare How do thestructures of ionic andcovalent compounds differ?What Are the Properties of Ionic Bonds?Ionic bonds form between oppositely charged ions.In general, atoms of metals, such as sodium and calcium,form positively charged ions. Atoms of nonmetals, suchas chlorine and oxygen, form negatively charged ions. Theattraction between ions with opposite charges holds ioniccompounds together.READING CHECK3. Identify What holds ioniccompounds together?Copyright by Holt, Rinehart and Winston. All rights reserved.Interactive Reader113The Structure of Matter

NameSECTION 2ClassDateIonic and Covalent Bonding continuedTRANSFER OF ELECTRONSIonic bonds form when one atom transfers electrons toanother atom. The atom that lost the electron has a positive charge. The atom that gained the electron has a negative charge. The figure below shows the transfer of anelectron from a sodium atom to a chlorine atom. Chlorineattracts electrons more strongly than sodium does. Twoatoms tend to form an ionic bond when one atom attractselectrons more strongly than the other atom.1e–EHHDBG@ EHL K 7e–8e–2e–8e–2e–4. Identify In sodiumchloride, which ion isnegatively charged and whichis positively charged?ElectrontransferredChlorine atomSodium atom8e–8e–2e––8e2e–Attraction5. Compare Describe theoutermost orbitals of Na and Cl .Positive sodium ionNegative chloride ionIonic bonds form when one atom transfers electrons to another.The result is two ions with opposite charges. The oppositelycharged ions attract each other.NETWORKS OF IONIC COMPOUNDSREADING CHECK6. Explain Why is thechemical formula for sodiumchloride NaCl, and not NaCl6or Na6Cl?There is no such thing as “a molecule of NaCl.”Sodium chloride is made up of a network of ions. In thenetwork, each sodium ion is surrounded by six chlorideions. Why, then, is the chemical formula for sodiumchloride not NaCl6? In sodium chloride, each chlorideion is also surrounded by six sodium ions. Thus, in asample of sodium chloride, there is one sodium ion forevery chloride ion.Different ionic compounds have different ratios of ions.For example, in calcium fluoride, the ratio of calciumions to fluoride ions is 1:2. That is, there are twice as manyfluoride ions in a sample as calcium ions. Why?Recall that calcium forms ions with 2 charges andfluorine forms ions with 1 charges. The total chargeof an ionic compound is zero. For the total charge tobe zero, the positive and negative charges must canceleach other.Copyright by Holt, Rinehart and Winston. All rights reserved.Interactive Reader114The Structure of Matter

NameSECTION 2ClassDateIonic and Covalent Bonding continuedCalcium ion, Ca2 Fluoride ion, F–One formula unitThe ionic compound calcium fluoride has twice as many fluoride ionsas calcium ions. Thus, the chemical formula for the compound is CaF2.CONDUCTING ELECTRICITYElectrical current is moving charges. The ions in asolid ionic compound are locked into place. Thus, thecharges are not free to move, and the compound cannotconduct electricity. However, when an ionic compounddissolves or melts, the ions are no longer locked in place.The ions are free to move. Thus, dissolved or meltedionic compounds can conduct electricity.7. Explain Why can a meltedionic compound conductelectricity, but a solid ioniccompound cannot?K I–READING CHECKWhen an ionic compound is solid, the ions arelocked in place.When the solid melts, ions can move morefreely and conduct electricity.I–K K I–H2OIons dissolved in a solvent can move freelyand conduct electricity.Copyright by Holt, Rinehart and Winston. All rights reserved.Interactive Reader115The Structure of Matter

NameSECTION 2ClassDateIonic and Covalent Bonding continuedWhat Are the Properties of Covalent Bonds?READING CHECK8. Define What is acovalent bond?A covalent bond forms when electrons are sharedbetween two atoms. Compounds that are made ofmolecules, such as water and sugar, have covalentbonds. Compounds that exist as networks of bondedatoms, such as silicon dioxide, are also held togetherby covalent bonds. In general, covalent bonds formbetween atoms of nonmetals.The figure below shows electrons shared by twochlorine atoms. Before the chlorine atoms bond, eachatom has seven electrons in its outermost energy level.By sharing a pair of electrons, both atoms can have fulloutermost energy levels.A single line between two atoms in a structuralformula represents a covalent bond. Each covalentbond indicates that two electrons are shared betweenthe atoms.Two of the electrons are inthe shared electron cloud.EHHDBG@ EHL K 9. Identify How manyelectrons does each linebetween atoms represent?7e –8e –2e –7e–8e–2e –8e–8e–2e –8e–8e–2e – Chlorine atomChlorine atomChlorine moleculeEach chlorine atom has sixelectrons that are not shared.10. Identify From wheredid the electrons that formthe covalent bond betweenchlorine atoms come?ClClOne covalent bond (two shared electrons)Two chlorine atoms share electrons equally to form a nonpolar covalent bond.MOLECULAR COMPOUNDSCovalent compounds made up of molecules are calledmolecular compounds. Molecular compounds can besolids, liquids, or gases. Most molecular compoundshave low melting points—generally below 300 C. When amolecular compound dissolves or melts, the moleculescan move more freely than they do in solids. However,unlike melted or dissolved ions, molecules cannot conductelectricity. This is because molecules are not charged.Copyright by Holt, Rinehart and Winston. All rights reserved.Interactive Reader116The Structure of Matter

NameClassSECTION 2DateIonic and Covalent Bonding continuedMULTIPLE BONDSSome atoms need to share more than one pair ofelectrons to fill their outermost energy �2e–2e–2e–2e–EHHDBG@ EHL K 11. Identify How many pairsof electrons are sharedbetween oxygen atoms in O2?Four electrons are in theshared electron cloud.OODouble covalent bondSix electrons are in theshared electron cloud.NN12. Identify How manyunshared valence electronsdoes each oxygen atom have?Triple covalent bondNotice that the covalent bond that joins the twooxygen atoms in the figure is shown as two lines. Thesetwo lines represent two pairs of electrons, or a total offour electrons. Two pairs of electrons shared betweenatoms are called a double bond.The covalent bond that joins the two nitrogen atomsabove is shown as three lines. These three lines representthree pairs of electrons. Three pairs of electrons sharedbetween atoms are called a triple bond.More energy is needed to break double and triplebonds than to break single bonds. A double bond isstronger than a single bond. A triple bond is strongerthan both single and double bonds. Double and triplebonds are also shorter than single bonds.EQUAL SHARINGWhen two atoms of the same element share electrons,they share the electrons equally. That is, the electronsspend equal amounts of time near the nuclei of bothatoms. For example, two chlorine atoms are exactlyalike. When they bond, electrons are equally attracted tothe positive nucleus of each atom. Bonds in which theelectrons are shared equally are called nonpolar covalentbonds.READING CHECK13. Identify Which bond isstrongest—a single, double,or triple bond?Copyright by Holt, Rinehart and Winston. All rights reserved.Interactive Reader117The Structure of Matter

NameSECTION 2ClassDateIonic and Covalent Bonding continued8g i XVa I] c c\14. Explain In a moleculeof ammonia, NH3, threehydrogen atoms are attachedto one nitrogen atom. Are thebonds in ammonia polarcovalent or nonpolarcovalent? Explain your answer.UNEQUAL SHARINGWhen two atoms of different elements share electrons,they do not share them equally. The shared electrons areattracted to the nucleus of one atom more than to theother. Bonds in which electrons are not shared equallyare called polar covalent bonds.In a molecule of ammonia, NH3, electrons are not shared equally.In general, electrons are more attracted to elementslocated farther to the right and closer to the top of theperiodic table. For example, within a molecule of ammonia, NH3, the shared electrons are more attracted to thenitrogen atom than to the hydrogen atoms.8g i XVa I] c c\15. Infer Which elementwill attract electrons morestrongly—fluorine or carbon?Explain your answer.What Are the Properties of Metallic Bonds?Metals, such as copper, can conduct electricity whenthey are solids. Metals are also flexible, so they can bendand stretch.Atoms in metals pack tightly together. This happensbecause the nucleus of each atom strongly attractsthe electrons from a neighboring atom. These strongattractions are called metallic bonds. Because theatoms are packed so tightly, the outermost energy levelsof neighboring atoms overlap. Therefore, electrons arefree to move from atom to atom.What Are Polyatomic Ions?READING CHECK16. Identify What kind ofbond exists between atomsin a polyatomic ion?The ions we have looked at so far are monatomic.That is, each is a single atom that has gained or lost anelectron. However, some ions are made of groups ofatoms that are covalently bonded. This kind of ion is apolyatomic ion. In a compound, a polyatomic ion actsas a single unit. A polyatomic ion can form ionic bondswith other polyatomic ions or with monatomic ions.Copyright by Holt, Rinehart and Winston. All rights reserved.Interactive Reader118The Structure of Matter

NameSECTION 2ClassDateIonic and Covalent Bonding continuedSome Polyatomic Ions Hydroxide ion, OH 2 Carbonate ion, CO32 Ammonium ion, NH4 Many compounds you may use contain polyatomicions. For example, baking soda, NaHCO3, contains thepolyatomic ion hydrogen carbonate, HCO3 . Sodiumcarbonate, Na2CO3, which is used to make soaps andother cleaners, contains the carbonate ion, CO32 .Like other ions, polyatomic ions with oppositecharges can bind to form compounds. For example,ammonium nitrate, NH4NO3, is made up of positivelycharged ammonium ions, NH4 , and negatively chargednitrate ions, NO3 .PARENTHESES AND POLYATOMIC IONSWhy is the chemical formula for ammonium sulfatewritten as (NH4)2SO4 instead of N2H8SO4? Parenthesesshow you that the ammonium ion, NH4 , acts as asingle ion. The subscript outside the parentheses tellsyou how many of that particular polyatomic ion are inthe compound.Remember that the charge on a polyatomic ion appliesto the whole ion, not just the last atom of the formula.The ammonium ion, NH4 , has a 1 charge. This meansthat NH4, not just the hydrogen atom, has a positivecharge. This is why a polyatomic ion acts as a single unit.READING CHECK17. Identify What doparentheses around a groupof atoms in a chemicalformula indicate?OXYGEN-CONTAINING POLYATOMIC IONSMany polyatomic ions contain oxygen. The names ofmany polyatomic ions that contain oxygen end with -iteor -ate. A polyatomic ion with a name that ends in -atehas one more oxygen atom than one with a name thatends in -ite. For example, the chlorite ion has one feweroxygen atoms than the chlorate ion.Notice that the hydroxide ion, OH–, and the cyanideion, CN–, have unique names. These ions are not namedaccording to any general rule.8g i XVa I] c c\18. Apply Concepts Thechemical formula for thechlorate ion is ClO3 . What isthe chemical formula for thechlorite ion?Copyright by Holt, Rinehart and Winston. All rights reserved.Interactive Reader119The Structure of Matter

NameClassDateSection 2 ReviewSECTION VOCABULARYcovalent bond a bond formed when atomsshare one or more pairs of electronsionic bond the attractive force betweenoppositely charged ions, which forms whenelectrons are transferred from one atom toanothermetallic bond a bond formed by the attractionbetween positively charged metal ions and theelectrons around thempolyatomic ion an ion made of two or moreatoms1. Predict Would an atom of sodium and an atom of potassium join to form an ioniccompound? Explain your answer.2. Explain Why are electrons shared equally in oxygen, O2, but not in carbonmonoxide, CO?3. Describe Examine the structural formula below. Complete the table to describethe bonds between atoms in the compound.OCClBonded atomsClNumber of sharedelectronsSingle, double, ortriple bond?Polar or nonpolar?C—OC—Cl4. Identify Which of the bonds in calcium hydroxide, Ca(OH)2, are ionic and whichare covalent?5. Identify Which of the following substances will conduct electric current:aluminum foil, sugar (C12H22O11), or potassium hydroxide (KOH) dissolved inwater? Explain your answer.Copyright by Holt, Rinehart and Winston. All rights reserved.Interactive Reader120The Structure of Matter

Ionic and Covalent Bonding continued The ionic compound calcium fl uoride has twice as many fl uoride ions as calcium ions. Thus, the chemical formula for the compound is CaF 2. Calcium ion, Ca2 Fluoride ion, F– One formula unit CONDUCTING ELECTRICITY Electrical current is moving charges. The ions in a solid ionic compound are locked into .

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